I have been working on a Zigbee device built around the ESP32 H2, and the more time I spend on it, the more I realise that the device itself is only half of the story. A Zigbee device is only as good as the network it joins, and the heart of that network is the coordinator. Right now my home runs on a SONOFF Zigbee dongle plugged into the machine that hosts Home Assistant, and that works, but it has limits. So in this article I am taking a proper look at the SLZB Ultima from SMLIGHT, a gateway that can run several radio protocols at once and act as more than one thing on your smart home network.

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What the SLZB Ultima Actually Is

The short version is that this is a network connected gateway for your smart home, and the interesting part is that it has two radios inside at the same time. With the add-on modules that SMLIGHT sells for it, you can push that up to four radios in one box. Out of the box it can run as a Zigbee coordinator and a Thread router simultaneously, which is something most of the little USB dongles simply cannot do.

The idea behind the device is that it does not have to sit next to your server. Your Home Assistant machine is usually tucked away in a cupboard or a rack, which is the worst possible place for a radio. The Ultima connects over your network, so you can put it somewhere central in the house, on a shelf or near the TV, and get much better coverage for all your battery powered sensors and switches. That alone is a good reason to move away from a dongle hanging off the back of a server.

On top of the radios it has an infrared receiver and an infrared transmitter, so it can work as an IR hub for old remote controlled gear, and it has a Bluetooth radio inside so it can work as a Bluetooth proxy too. That is a lot of jobs for one small box.

What Comes in the Box

My unit arrived with a note on top telling me that it ships with an initial firmware and that I should update it for the best performance. That is a nice touch, because it sets the expectation right away that the first thing you do is flash it.

Inside I found the Ultima model 3 itself along with two antennas, one for each of the two radios. You can run both radios as Zigbee, or you can run one as Zigbee and the other as Thread. The antennas had been taped in place for shipping and mine had come loose in transit, so they were rattling around a bit, but nothing was damaged.

I also received a set of add-on modules to go with it. There is a Z-Wave module, a 4G module that sits inside the case and gives you a backup internet connection, a power over Ethernet add-on, and a microphone add-on. The 4G and Z-Wave modules come with their own antennas, one labelled 4G and the other labelled 900 MHz for the Z-Wave radio.

For connectivity, the back of the unit has the power USB port and the network port, and there is a headphone style audio jack there too. The front has two USB-C ports and there is a USB-A on the side. Those USB ports on the front are also where some of the additional radios connect.

Opening It Up

I wanted to see the board and show how the add-on modules install, so I opened the case. There are no screws anywhere on this thing, so the only way in is to pry the plastic clips apart with a spudger. I will be honest, I do not love that choice. This is a user serviceable device that is designed to have modules added to it, and for a device like that I would much rather have four screws than a set of clips I have to fight with. There is one big clip at the front near the USB ports that gave me real trouble, and doing all of this in front of a camera is not fun.

Once the back case comes off, the board lifts out of the front case in one piece. The front of the board carries a set of RGB LEDs, which is why the front of the case has a transparent panel over it.

A Look at the Board

The main processor sits in the middle of the board with the LEDs at the front edge. Off to one side there is what I believe is the Bluetooth module, and it looks like there is a pad for an external antenna if you wanted to add one. The infrared transmitter and receiver are both mounted at the front so they can see through the case. There is also a row of pins on the board where the add-on modules plug in.

Flipping the board over reveals the two radio modules. The first one uses the CC2674 from Texas Instruments and the second one is labelled MG24 A20J1, which is the Silicon Labs EFR32MG24. Both of them can run Zigbee, and the EFR32 is the better choice for Thread, so the sensible setup is to dedicate one module to Zigbee and the other to Thread. You get that straight out of the box with no extra hardware.

The thing that genuinely surprised me is an expansion port on the board. It gives you 5 volts and ground along with I2C, and there are extra pins broken out that you can use as general IO. I have not seen any other Zigbee coordinator offer dedicated IO pins like this, so that is a nice piece of forward thinking from SMLIGHT.

Installing the Add-On Modules

The add-ons are designed to be as simple as possible. Each module has pass through headers, so you line it up with the matching connector on the board and push it down, and that is it. The board has markings printed on it so you know which module belongs where, and once a module is seated it is already connected with nothing else to configure at the hardware level.

I fitted the power over Ethernet board first, then tried the 4G board on its port. There is one important warning with the 4G module. Install the SIM card before you put the module in and close the case, because there is no access port on the side of the enclosure to reach the SIM slot later. If you forget, you are prying those clips open all over again. The case also has a knockout for the 4G connector so the antenna can stick out properly.

In the end I decided to leave the power over Ethernet module installed even though I am not using PoE right now, and I left the 4G module out for the moment. Then I closed the case back up.

First Power On

Before you plug in any device like this, fit the antennas. This is true for every radio device, not just this one. Running a transmitter with no antenna attached can damage the radio, so make it a habit.

With the antennas on I connected the power and the network cable. I looked for Wi-Fi during setup and it did not connect on its own, so I went straight in over Ethernet. The device supports mDNS, so I simply opened slzb-ultima3.local in the browser on my computer and the interface came straight up with no IP hunting needed.

The very first thing the interface told me is that the firmware on the device is still a beta release and needs updating. I went to settings, firmware update, and checked for updates. It took a few minutes and the whole thing was handled automatically by the device, which is exactly how a firmware update should work.

Going Through the Interface

The main dashboard shows the connection status, confirming that I was online through the LAN, and it shows the modes and settings for each of the attached devices. It correctly identified that I had not installed the 4G module. There is a Wi-Fi section that is switched off by default and can be turned on, and the mDNS setting that I had just used to reach the page.

Down the right side there is live information about each radio. It shows the core type, the core temperature of each chip, the firmware version on each radio and how each one is configured, and it all updates by itself. Below that is the Ethernet status and the Wi-Fi status.

Radio Modes

Under the mode section you choose what each radio module does. You pick which one runs Zigbee and which one runs Thread, and you set how each of them operates. The recommended setup is one radio on Zigbee and the other as a Thread border router. What I really appreciate here is that each option has a small popup explaining exactly what happens when you enable or disable it, which takes a lot of the guesswork out of configuring a device like this.

The same section also holds the configuration for the third radio slot, the Z-Wave module I have not installed yet, plus switches for Wi-Fi, the USB connection and an internet to Wi-Fi bridge.

Zigbee Hub Mode

This is the mode that caught my attention the most. The Ultima has a Zigbee hub mode where it talks to your devices directly, with no Home Assistant or other server sitting behind it. For a small network, or for a dedicated corner of the house that only has a handful of devices, the Ultima can be the whole smart home on its own. There is even a way to add scripts and automations to it, so the logic runs on the gateway itself. I am going to skip past it here because it genuinely deserves its own video where I set it up properly with a few real devices and see how far it goes.

Network and MQTT

The network tab has the standard settings you would expect. You can disable mDNS, and DHCP is enabled by default with the option to switch to a static IP. The Wi-Fi settings live here too, greyed out until you enable Wi-Fi.

There is also an MQTT section, and this is more capable than I expected. The device can connect directly to your MQTT broker, including brokers using SSL, so everything on the gateway becomes reachable over MQTT. On top of that it carries the configuration for Zigbee2MQTT and it generates the config for Home Assistant for you, which saves a fiddly manual step.

There is a menu for all the 4G settings as well, disabled on my unit since the module is not fitted.

Infrared

The infrared section has learn and replay options. I grabbed a basic remote from the bench, pointed it at the gateway and hit learn, and the raw captured signal appeared on screen straight away. From there you can fire it back out through the transmitter.

Getting that on camera turned out to be harder than capturing it. Infrared is invisible to the eye and my camera would not pick it up at all. I tried a phone camera next and only got a faint flash when I moved in very close. It works, the camera just struggles to prove it.

Audio and Lighting

The audio section can play a stream on the 3.5 mm jack on the back, either from a URL or from a file stored on the device. More useful day to day, there is a built in buzzer with a set of melodies and chimes, including a siren and a success tone. Trigger those from Home Assistant and you have a simple notification device sitting in the middle of your house that can tell you when something happens.

The ambient light section gives you full control over the RGB LEDs at the front. You pick the colour, you pick an effect, and you can set both the speed and the intensity. I set it to rainbow and it looks great. Pair that with a few automations and you can have different light schemes for different states in your home.

Security and Remote Access

There is a security section where you can restrict access to specific IP addresses, and you can connect the gateway to a VPN. If your Home Assistant instance lives somewhere else, you can set up dynamic DNS and reach the gateway remotely.

There is also USB pass through, which makes a USB device connected to the gateway available over the network. The examples given are for various adapters, but it made me wonder what else you could hang off it. A printer, maybe. That is another thing worth exploring properly at some point.

Bluetooth

For Bluetooth you have two choices. You can run the built in proxy from the Ultima firmware as it ships, or you can flash the whole gateway with the ESPHome Bluetooth proxy firmware and turn it into a dedicated Bluetooth proxy.

Scripts, Automations and an AI Assistant

This is where I think the gateway really shines. You can write your own scripts and your own code that run on the device, triggered at startup or on specific events. There are integrations available for Telegram, WhatsApp, Slack and others, and it looks like you can add your own.

The part that genuinely surprised me is the built in AI assistant. You supply your own API key for the model you want to use, and from there it can help configure your automations and integrations and set up how the device behaves. That opens the door for people who are not comfortable writing code to still build useful automations running directly on the gateway.

General Settings

The general settings let you name the device, set the flash mode and restart individual modules. Firmware update lives here, as does backup and restore for all your settings, which is a very welcome feature on a device with this many options. There is LED control including a night mode that turns the LEDs off during set hours so they do not light up your living room while you sleep. You also get time zone and NTP server settings, logs and a debug view for tracking down problems, and at the bottom a reboot button and a way to report bugs or send feedback straight from the firmware.

Final Thoughts

SMLIGHT has a dedicated page for the Ultima on their website, and I would recommend a look before you buy. They have documented every single part on the board and explained what it does and which scenarios it helps with, which is more effort than most companies put into a product page.

For me the SLZB Ultima is a device worth having. Two radios out of the box, room for four, a proper expansion port with IO, infrared, Bluetooth, audio, scriptable automations and an AI assistant is a lot of capability in one small box, and moving the radio away from the server cupboard is worth it on its own. I have only scratched the surface here and I will be spending a lot more time with it over the coming months, especially with the standalone Zigbee hub mode and the 4G module.

If you enjoyed this look at the Ultima and want to see more smart home builds and teardowns, subscribe to the Taste The Code YouTube channel so you catch the follow ups when I put this gateway through its paces.

Links And Resources

• SLZB Ultima Product Page (SMLIGHT)
• Z-Wave Add-On Module
• 4G Add-On Module
• Power over Ethernet Add-On Module
• Microphone Add-On Module

Other gateways and products from SMLIGHT:

• SLZB-06U - https://s.click.aliexpress.com/e/_c3SGRzNL
• SLZB-06M - https://s.click.aliexpress.com/e/_c401VJO5
• SLZB-06P7 - https://s.click.aliexpress.com/e/_c35WFwPF
• SLZB-06P10 - https://s.click.aliexpress.com/e/_c3FYrUT7
• SMLIGHT WLED Controller - https://s.click.aliexpress.com/e/_c2RxOlcp
• A1-SLWF-11 WIFI ESP8266-Based Addressable-WLED Controller - https://s.click.aliexpress.com/e/_c4TegYCl

Other tools and materials:

• SONOFF Zigbee 3.0 USB Dongle Plus - https://s.click.aliexpress.com/e/_c3uO7ZVx
• ESP32 H2 Board - https://s.click.aliexpress.com/e/_c4MvoOSt
• JCD Soldering Station - https://s.click.aliexpress.com/e/_c3AJ2Tvb
• Bench Power Supply - https://s.click.aliexpress.com/e/_c3PEDIhn
• Digital Multimeter - https://s.click.aliexpress.com/e/_c4LoV9Tr